Fix double-quoted multilinestring issue.

An Oozie case statement can be multiline and even with simple expression users
often put the el expression on its own line. If not handled carrefully it leads to
an invalid file. Indeed, the DOT language specifies that a double-quoted string
"allows single logical lines to span multiple physical lines using the standard
C convention of a backslash immediately preceding a newline character."

Usually EL expressions are short enough to be merged as a single line. If
required we can use a more sophisticated algorithm to decide if the lines
should be joined or not.